Astronomers have directly measured the speed of superheated gas emanating from the core of M82, a starburst galaxy, using data from the Resolve instrument aboard the XRISM (X-ray Imaging and Spectroscopy Mission) spacecraft.
The gas is moving at speeds exceeding 2 million miles (over 3 million kilometers) per hour. This observation suggests that this hot gas is the primary force behind the cooler, larger-scale galaxy wind that extends up to 40,000 light-years from M82's core.
Erin Boettcher, an astrophysicist at the University of Maryland, College Park and NASA's Goddard Space Flight Center, stated that while classic models predict shock waves from star formation and supernovae heat gas to initiate powerful winds, previous instruments could not measure the necessary velocities. The new data shows gas moving faster than some predictions, sufficient to propel the wind to the galaxy's edge.
This research, led by Boettcher, was published in Nature on March 25. The XRISM mission is a collaboration between JAXA, NASA, and ESA.
M82, also known as the Cigar galaxy, is located 12 million light-years away and forms stars approximately 10 times faster than the Milky Way. Its extended cool wind has been studied by various missions, including NASA's Chandra, Webb, Hubble, and Spitzer space telescopes.
The Resolve instrument's capabilities allowed researchers to precisely measure the hot wind's speed by analyzing an X-ray signal from superheated iron in the galactic center. The iron's X-ray light indicated a temperature of 45 million degrees Fahrenheit (25 million degrees Celsius). The broadness of the iron spectral lines, due to Doppler shifting, revealed the gas velocity, confirming it was slightly faster than anticipated.
These findings suggest that the hot wind, combined with its high temperature, is powerful enough to generate the cool wind without requiring cosmic rays as a main source of outward pressure, though cosmic rays may still contribute.
The research indicates that M82's center expels enough gas annually to form seven stars the mass of our Sun. However, there is a discrepancy: if the wind maintains the measured speed, it should power the cooler wind by expelling four solar masses of gas per year.
Co-author Edmund Hodges-Kluck noted that XRISM data suggests more gas is moving outward, raising questions about the fate of the additional three solar masses.
These XRISM observations are expected to refine models of starburst galaxies, aiding in future scientific inquiries. Skylar Grayson, a graduate student at Arizona State University, highlighted that these observations allow for testing and improving starburst galaxy models developed as early as the 1980s.